For over 10 years there have been no clinical studies about adult-onset Still's disease (AOSD) in Japan. We aimed to investigate recent clinical features and treatment of AOSD and to evaluate the efficacy of cyclosporin A (CyA) in the treatment of AOSD. The data from 34 patients with AOSD who were admitted to our hospital between 1994 and 2007 were analyzed retrospectively. Of several immunosuppressive agents, the efficacy of CyA given to seven patients was precisely evaluated. Clinical features observed in this study did not differ from those in our previous study, and serum ferritin levels were elevated in all the patients. Among immunosuppressive agents CyA, used concomitantly with corticosteroids (CS) for seven patients with severe AOSD, proved to be very effective. The disease was led to remission promptly by CyA in six patients, and all the patients except one experienced no recurrence. These results suggest that CyA can be one of the potent candidates to be used next to CS for patients with AOSD that is resistant to CS.